Sprinkle the sugar evenly over the bottom. Allow it to melt and begin to caramelize. If sugar crystals begin to form along the side you can use a wet pastry brush to brush them down.
Add the orange juice, butter, and zest, and stir to combine. Allow the mixture to come to a simmer and reduce to thicken, about 5 minutes.
Quickly dip a crepe into the sauce making sure both sides are coated. Fold into a triangle.
Repeat with the remaining crepes.
Add the Grand Marnier. Use a kitchen lighter or long match to ignite the sauce.